The present inventors have disclosed in JP, 8-34764,A that an S,S-ethylenediamine-N,N'-disuccinic acid iron ammonium salt, which is a compound useful for photographic bleaching and the like, has a high biodegradability. However, in a production process for producing the disclosed compound, it was necessary to obtain a highly viscous and highly slurry concentrate because of the very high solubility of the desired compound, in order to obtain the desired compound in high yield. Therefore, there has been a desire for a production process having a higher productivity as an industrial production process. A process for obtaining the desired compound by a concentration to dryness or a continuous hot gas drying has achieved an improvement in the yield but has been disadvantageous in product quality that, for example, powders obtained by said process were so poor in shelf stability that it was colored or was deteriorated in solubility.
Unlike a production process using an inorganic salt such as iron sulfate, a production process using iron oxide was expected to make it possible to obtain a desired compound having a relatively high purity by evaporating a reaction solution to dryness as it was, unless starting materials are decomposed. However, when a meso/racemic mixture of ethylenediamine-N,N'-disuccinic acid was used, a product obtained by such a process had a very high hygroscopicity in some cases and moreover its purity was not sufficient. In addition, also when S,S-ethylenediamine-N,N'-disuccinic acid was used, the resulting solid had a low stability, for example, it was colored or gave an insoluble material with a lapse of time. Furthermore, the solid had a low purity and the mass balance of the S,S-ethylenediamine-N,N'-disuccinic acid used was markedly unsatisfactory.
An object of the present invention is to solve such problems and provide an S,S-ethylenediamine-N,N'-disuccinic acid iron alkali salt having a high storage stability and a process for producing the same in high yield.